A Gecko-Inspired Soft Passive Gripper

Abstract

This paper presents a soft passive gripper consisting of six fluidic soft bending actuators arranged in a star-shaped manner. The actuators are oriented such that, upon pressurization, they bend against gravity. Gripping is realized by a commercial tape with mushroom-shaped adhesive structures that is glued to the bottom patches of the gripper. In this way, the object is released by peeling away the actuators from the object's surface. In contrast to active grippers, which require continuous pressurization during gripping and holding, the presented passive gripper only requires energy for the release process. However, due to its working principle, the gripper is restricted to only flat objects or objects with at least one flat surface.

Keywords: fluidic elastomer actuators; gecko-inspired adhesive; soft passive gripper; soft robotics.

Figure A1

Free-body diagram of the infinitesimal element.

Figure A2

Moment arms of the forces.

Figure A3

Graph of Equation (A30).

Figure A4

Fabrication steps of a soft bending actuator with a prepreg as strain-limiting layer ($\alpha =0°$): (a) assembly of the mold, (b) mixing of elastomer, (c) filling the mold, (d) extracting the cured part from the mold, (e) placing the cured part on the prepreg layer.

Figure 1

Partially cut fPN soft bending actuator.

Figure 2

Attachment and detachment process of a soft bending actuator as soft gripper: (a) attached, uninflated; (b) detached, inflated.

Figure 3

Variation of the number of soft bending actuator branches in the gripper: (a) four branches, (b) six branches.

Figure 4

Variation of the shape of the soft bending actuator branches in the gripper: (a) flat, (b) sloped (in the displayed configuration, $\alpha$ is negative).

Figure 5

Graph of Equation (1).

Figure 6

Scanning electron micrograph of mushroom-shaped adhesive microstructure (MSAMS). Inset shows an individual MSAMS in contact with smooth glass substrate. SH, shaft; CL, contact lip; NN, narrowed neck. Used with permission [18].

Figure 7

Experimental results of the detachment pressures for different slopes of soft bending actuators.

Figure 8

Sequential detachment of air chambers of an actuator with $\alpha =+20°$: (a) attached, (b) most outer air chambers detached, (c) first three outer air chambers detached, (d) completely detached.

Figure 9

CAD model of the final design of the passive gripper with side extensions ($\alpha =-20°$): (a) isometric view, (b) bottom view.

Figure 10

Operation of the passive gripper: (a) attached, (b) carrying, (c) detached.